After taking a note of all the things said here, two other things come to mind.
The first is how easy it is to exploit the machine. With Windows IE exploits, you don't need access to the machine. Whereas (correct me if I'm wrong here), with Linux you actually need some kind of access to run most of the exploits.
The other thing that comes to mind is intent. Almost every script kiddie out there wants to get into a Windows machine while only experienced users and relatively good hackers try to get into a Linux machine.
And, another thing, how many capable hackers/crackers do you know that are capable of getting on a Linux machine with malicious intent. I'm not saying they don't exist. All I'm saying is that their number is less than the number of AOL kiddies out there.
Any way, just my opinion,